Some fasteners were used on bed to allow knock down and headboard adjustment. The short rail tenons glued into each corner post have a square nut let into them. The square nut accepts a bolt from the long rails. The connection is totally concealed and has remained sturdy through house moves and all these years. Somehow I didn’t get a picture of this neat detail before gluing it all together.

Here’s a tip for anyone that wants to try a captive nut – thread the bolt into the corner post before glue dries on the threads of the nut. Remove the bolt before the glue totally sets. If you get glue on the threads it’s a nightmare to get the bolts threaded in and you can’t access the nut because it’s glued inside the corner post by that point. Don’t ask me how I know, lol.